This invention relates generally to a memory lock device and method and more particularly to a memory lock device and method for a text entry system.
Recent advances in memory systems for text entry systems such as those used in shorthand machines or other text editing machines have greatly enhanced the ability of the user to store data which is entered by means of a keyboard into a permanent storage device such as a floppy disk or a fixed disk.
Although existing memory systems provide the user with significant benefits they are not without disadvantages. For example one problem with existing memory devices is related to the ability of the memory to maintain the integrity of previously entered data in the event the system "crashes". Such system crashes may occur, for example, because of hardware failure, software malfunctions or more commonly if the power source such as the batteries in the device inadvertently fall out or are removed from the device.
Therefore, such devices typically include non-volatile or battery backed-up portions of memory into which the data associated with keystrokes from the keyboard is entered. In this manner if the text entry system suffers a loss of power, a non-volatile state of the memory will be maintained thereby preventing data from being lost if the system loses power.
An example of a device in which data is written to a non-volatile memory is given in U.S. Pat. No. 4,447,887 (Imazeki). This reference discloses a method and system for writing data in a non-volatile memory in which the writing of one access unit of stored data is executed by erase and write cycles such that the stored data is protected in the event of an interruption in electric power. In this system data is stored in a data storage area of a non-volatile memory and the data is rewritten into second data. Subsequently either the original or the second data is stored in a save area of the non-volatile memory after which the original data in the data storage area is erased. The second data is then written into the data storage area to complete the rewrite operation. In this manner, if a power interruption occurs before the information stored in the data storage area is taken out and preserved in a save area the information will remain in the storage area. On the other hand, if the power interruption occurs after the information stored in the data storage area has been taken out and preserved in the save area, but before the write cycle of the rewrite process has been completed, the information will remain in the save area. A restoration process may then be executed when the power is restored to restore the information in the save area to the data storage area.
An example of a system which incorporates a battery backed up memory is disclosed in U.S. Pat. No. 4,178,634 (Bartlett). This reference discloses a programmable logic controller which includes a scratch pad memory for the temporary storage of data which is divided into two sections. One of the memory sections is completely reset when the power is turned on while the other of the memory sections is maintained in its programmed state regardless of power failure. In the system disclosed in this reference the retentive portion of the scratch pad memory can only be reset by the actuation of a reset button when the power to the unit is turned "off".
These non-volatile or battery backed up memory systems, however, do not provide a complete solution to the occurrence of crashes in the system. For example, when a system crashes, data may be inadvertently written by the microprocessor to the memory locations which contain the pre-stored data from the keystrokes. In such an event the integrity of the data contained in the memory (which may correspond to the data entered from the keystrokes) would not be maintained.
It is therefore desirable to provide a system in which data which has been written into memory will remain intact even if the system crashes. It is desirable to assure not only that data will not automatically be erased if a crash occurs, but that data will not be altered when a crash or other system interrupts occurs.
Therefore in view of the above it is a primary object of the present invention to provide a system and method with which the integrity of data which has been previously written into a retentive type memory will be maintained.
It is a further objection of the present invention to provide a memory system for use in a text entry system which will prevent data which is not associated with a keystroke from being inadvertently entered into memory.
It is still the further object of the present invention to provide a lockable memory which will only allow predetermined data to be entered and prevent inadvertent alteration of previously entered data.